Two-stroke engines are widely used in various applications, such as for snowmobiles. The high power-to-weight ratios that these engines provide make them desirable. However, such engines typically emit greater amounts of pollutants, such as hydrocarbons and carbon monoxide. Efforts to reduce harmful emissions have included the use of various fuel injection systems. A standard fuel injection process employs a throttle body with a fuel and oil injection into the air flow. The flow then proceeds to the crankcase and into the cylinder under action from the piston. This may be somewhat cleaner burning than a carbureted system with a better control of the fuel delivery.
A semi-direct fuel injection process has also been developed involving injection of the fuel directly into the cylinder while channeling an air-oil mixture through the crankcase, through transfer ports then into the cylinder. Such a system may decrease emissions, but may have the effect of decreasing the peak horsepower produced at wide open throttle (WOT). Some of the loss of horsepower in such semi-direct and direct injection systems may stem from the higher crankcase and air intake temperatures that result. Feeding fuel through the crankcase tends to aid in cooling of the case. Furthermore, crankshaft bearing lubrication and piston and ring wear can be a problem with direct injection systems.